1. Field of the Invention
The invention lies in the field of conveying technology, and generally relates to a gripper for gripping and for the held conveying of objects, wherein the gripper includes a control element for actuating the gripper. The invention, moreover, relates to a conveying installation with a plurality of grippers with control elements for actuating the grippers.
2. Description of Related Art
Different examples of a gripper particularly suitable for gripping and conveying spatially extended, symmetrical objects, objects with a holding ring, hollow objects, and objects with different shapes and/or sizes are described in the following sections for a better illustration of the invention. The gripper in particular is suitable for gripping and conveying preforms for the production of receptacles of plastic, e.g. PET bottles.
Such grippers, for example, are applied, in order to convey preforms for blow moulding of containers of plastic and the manufactured containers, between different stations of a blow moulding installation. The preforms are hollow bodies of a thermoplastic plastic with an essentially rotationally symmetrical shape that are open at one side. As a rule, they include a thread and a holding ring.
Known grippers for preforms are designed in the manner of a pincer. The gripper jaws are arranged in a plane that lies perpendicularly to the rotation axis of the preform. They engage below the holding ring in the manner of a fork, by way of approaching them from the side. Conveying devices with such grippers therefore require relatively much space in the receiving region. The gripper jaws, in the region, in which these grip the object (clamping region) have a concave shape and are thus adapted to the cylinder-like shape below the holding ring. Objects with different diameters, however, can thus only be gripped within a certain maximal and minimal diameter. Examples for known preform grippers are described in US 2010/0278959, U.S. Pat. No. 6,612,634 or DE 10325693. Clamping mandrels are alternatively applied and these can be inserted into a mouth region of the preform for holding.
A gripper for gripping flat products, in particular printed products, and which includes a gripping body, a stationary and a moving gripper jaw is known from U.S. Pat. No. 4,921,294. The construction is mirror-symmetrical. The movable gripper jaw is formed by a mirror-symmetrical wire bow of spring steel. The wire bow in its end regions is shaped in each case into a helix. Moreover, it forms two holding tongues, departing from the helices. These holding tongues are orientated perpendicularly to the axis of the helices and are spaced from one another. The bow between the holding tongues is bent such that it forms an elongate, straight bow part that is located in the proximity of the common axis of the helices and acts as a pressing element. The helices are stuck onto pivots that are arranged on the gripper body at sides lying opposite to one another and that are aligned with one another. The wire body is biased against the stationary gripper jaw by way of the helices being fixed in the gripper body. A pivot axis is defined by the pivot, about which the gripper jaw can rotate. The gripper jaw is actuated by two control elements that each press onto the wire bow in the region of the holding tongue. These control elements press the movable gripper jaw away from the fixed gripper jaw when they are commonly actuated. For this, they are biased towards the moveable gripper jaw.
This design, due to the shaping of the bow with two projecting tongues and an elongate pressing element is adapted to flat objects and is not suitable for conveying spatially extended objects with a different shape. The actuation mechanism consists of several parts and is therefore complicated to manufacture and maintain.
The grippers, which are mentioned hereinafter as examples, serve for a better illustration of the invention and are designed according to a patent application of the same applicant that is not yet published. The grippers provide a conveying device and an operating method, with which device or method the disadvantages mentioned above are avoided. The gripper in particular is suitable for reliably gripping and conveying spatially extended objects with a different shape, e.g. preforms. The gripper is simple and inexpensive to manufacture and is robust as possible.